Poop-throwing chimps provide hints of human origins

Pick up an object that's close at hand. Throw it at something,
or even someone -- but gently, of course. You've just reenacted
what appears to be a pivotal stage in human evolution, when a
propensity for projectiles shaped cognitive powers that later
became language and symbolic thought.

That, at least, is one hypothesis for how humans became so
smart. And now researchers have found support in chimpanzees, among
whom the ability to throw goes hand-in-hand with increased
intelligence and brain development.

"Imagine you're an early hominid throwing at a rabbit. There's increased selection for the cognitive demands
of throwing, and that has some consequences for the development of
the brain," said psychologist William Hopkins
of Emory University. "That's where the throwing part becomes
really interesting."

In a study published in the January Philosophical Transactions of the
Royal Society B, Hopkins and colleagues tracked several
years' worth of throwing behaviours in captive chimpanzees. ("If I
was going to get s**t thrown at me, I was going to get something
out of it," said Hopkins.) Chimps are the closest living ancestor
to humans, and the only species aside from ourselves in which
throwing is regularly seen.

The researchers were especially interested in relationships
between throwing, cognition and lateralisation, or the way certain activities are concentrated in the left or right
hemispheres of our brains. Language processing occurs in
the left side, which also controls our right hands; and most people
use their right hands to throw, as do chimpanzees.

While throwing at first might not seem demanding, coordinating
it requires intensive, on-the-fly calculations. An equation for
throwing a ball, for example, would include the distance to a
target, the ball's heaviness and the thrower's strength. A moving
target makes it even harder. Other psychologists and
anthropologists have put throwing at the beginning of a cognitive
cascade into higher-order thought, but Hopkins said his team is the
first to test this proposition.

From brain scans of chimps that threw most often and accurately,
Hopkins found heightened development in and connections between the
motor cortex, where physical actions are coordinated, and

, which in humans is central to speech production. Better
throwing meant more sophisticated, left hemisphere-reliant brains.

"It supports the idea that these areas could have been selected
for as a consequence of throwing," said Hopkins. "If you imagine
that throwing started off as left hemisphere-dominant, before the
emergence of speech, then speech and language would have co-opted
that side of the brain."

In behavioural tests, true-throwing chimps also proved
especially apt in social intelligence and communication.
Intriguingly, they fared no better than poor-throwing chimps on
physical problem-solving tests, suggesting that throwing behaviours
emerged not for hunting, as is commonly assumed, but to interact
with peers.

"Why did these chimps learn to throw in a captive context? I've
never in my life seen a chimp be given a banana for throwing s-t at
someone," said Hopkins. "The reward is not something food-based.
The reward is that they can control a person's behaviour. They get
a pile of something to throw, and usually the person tries to run.
The chimp learns, 'If I can do this, I can have some control over
the world outside my cage.'"

Comments

It's a fallacy to describe chimps as our ancestors. Humans and chimps are descended from a common ape ancestor which was neither a human nor a chimp, but quite a lot like both. In the intervening years we became modern humans and chimps became modern chimps. In this sense the two species are close cousins.